Page:The Oak.djvu/33

 large cotyledons, without tearing them away from the structures just described, he will find that each is attached by a minute stalk to a sort of ridge just beneath the tiny plumule; this ridge is sometimes termed the collar. He will also see that the plumule and radicle fit closely into a cavity formed by the two cotyledons, and so do not interfere with the very close fitting of their two flat faces.

Summing up these essential features of the structure of the ripe acorn and its contents, we find that the fruit contains within its pericarp (which is a more or less complex series of layers, of which the outermost is hard) the seed; that this seed comprises a membranous testa inclosing an embryo; and that the embryo is composed of two huge cotyledons, a minute radicle, and a still more minute plumule; and that the tip of the radicle is turned towards the pointed end of the acorn, lying just inside the membranes.

Leaving the details of structure of the membranes until a later period, when we trace their development from the flower, I must devote some paragraphs to a description of the minute anatomy and the contents of the embryo as found in the ripe acorn, so that the process of germination may be more intelligible. Thin sections of any portion of the embryo placed under the microscope show that it consists almost entirely of polygonal chambers or cells, with very thin membranous walls, and densely filled with certain granule-like contents. These polygonal cells have not their